1. Field of the Invention
The invention relates to the recovery of heavy oil deposits, and particularly relates to improvements in fracture-assisted steamflood technology.
2. Brief Description of the Prior Art
There are many subterranean formations containing heavy oil deposits throughout the world from which the oil cannot be recovered by conventional means because of the high viscosity of the heavy oil deposits.
One technique which has been developed for recovering this heavy oil involves steamflooding through a generally horizontal hydraulically induced fracture network. The assignee of the present invention has recently developed such a fracture-assisted steamflood technology as is disclosed in detail in U.S. Pat. No. 4,265,310 to Britton et al., the details of which are incorporated herein by reference.
The fracture-assisted steamflood technology disclosed in the Britton et al. '310 patent consists of four distinct phases. Those phases are producer stimulation, preheat, matrix steam injection, and the heat-scavenging phase.
In the producer stimulation phase, the production wells are notched and horizontally fractured. Steam is injected through the notch at high rate and then, after perforation of the producers, over the entire reservoir interval.
The preheat phase is initiated by fracturing the central injection well and injecting steam at a rate and pressure sufficiently high to keep the horizontal fracture parted. Heavy oil production begins in this phase.
Once a heated link is established between the injection and production wells, the injector is perforated over the entire reservoir interval and steam is injected at a reduced rate during the matrix steam injection phase.
After a predetermined steam slug is injected, warm water is injected to recover heat and mobile heavy oil from the reservoir in the heat-scavenging phase.
The assignee of the present invention has performed two field pilot tests of the basic Britton et al. '310 process, and the results of those tests have been published in Society of Petroleum Engineers of AIME Paper No. SPE 13036, titled "The Saner Ranch Pilot Test Of Fracture-Assisted Steamflood Technology", by Stang et al., presented at the 59th Annual Technical Conference and Exhibition held at Houston, Tex., on Sept. 16-19, 1984, and in Journal of Petroleum Technology, March 1983, page 511-522, "The Street Ranch Pilot Test Of Fracture-Assisted Steamflood Technology" by Britton et al.
Although the two pilot tests described in the two above-referenced articles have shown the process of the Britton et al. '310 patent to be technically a success, it is recognized that it is important to improve as much as possible upon the efficiency of that process in order to make it economically successful.